1. Field of the Invention
The present invention generally relates to pumps for transferring and/or injecting fluids into a well and/or pipeline. More particularly, the invention relates to a surface-located pumping apparatus that reduces environmental hazards associated with pumps.
2. Background of the Related Art
In oil field applications fluid, like water or oil, is often pressurized and moved either between surface locations or is moved from a surface location to at least one downhole location. For example, there are instances where collected oil must be transported to a remotely located processing facility. In other instances, water is pumped down an injection well for disposal or for maintaining or increasing reservoir pressure in enhanced recovery operations or to encourage the flow of oil in underground formations to another well for recovery. In still other instances, pressurized water is injected into a wellbore to become mixed with oil and bring the oil to the surface of the well where it is separated from the water and collected.
Pumping oil out of a well that does not have adequate natural formation pressure is conventionally done through the use of an electric submersible pump located in the wellbore. The pumps operate at the end of a tubular string and include a pump and an electric motor along with a source of electrical power supplied from the surface to operate the electric motor. Because they operate in fluid at the bottom of a wellbore, electric submersible pumps are necessarily more expensive than conventional surface-mounted pumps. Additionally, repair or replacement of a submersible pump requires the removal of the entire pump assembly, which requires equipment, personnel, time and results in down time for the well.
In order to avoid the expense and problems associates with submersible pumps, jet pumps have been used in wellbores and are operated by surface-mounted equipment. The jet pump operates using the energy provided by fluid pumped under high pressure (power fluid) through them. A nozzle in the jet pump narrows the power fluid stream, draws in well fluid and carries it to the surface. If the power fluid is miscible (i.e., an oil) it will blend with the crude oil. If it is a non-miscible fluid such as water, it will separate easily at the surface. In either case, power fluid is usually separated from the produced liquid and then returned to the high-pressure pump for another trip downhole. Because positive displacement pumps are subject to leakage and because many wells are operated today in environmentally sensitive and remote jurisdictions, like Alaska, other types of pumps have been utilized at the surface of a well to operate jet pumps in a wellbore. In one example, a horizontal pump assembly including a standard industrial motor and an electric submersible pump is used at the surface of the well to operate a jet pump downhole. The advantage of the surface-mounted pump is that the motor is less expensive than a downhole motor and the apparatus can be accessed for repair or replacement without pulling it out of a wellbore.
All surface mounted pumping arrangements are subject to at least some leakage. In some environmentally sensitive areas, the entire apparatus is enclosed in a large container that includes alarms, sensors and kill switches to detect the presence of and to contain leaks.
In order to reduce expense and containment costs related to surface located pumps in sensitive areas, a jacketed pump assembly has been utilized and includes a submersible electric pump assembly that is housed in a pressurized jacket. In this manner, all leaks from the apparatus are contained within the jacket and the jacket is filled with fluid to provide a source of fluid to the pump intake that is located in the jacket.
As one example, a multistage centrifugal pump is mounted at the surface adjacent to the well. The centrifugal pump is of a type that normally would be utilized in a vertical application within a well for pumping fluid from the well. The pump and related assembly are typically mounted in a pressure vessel or jacket and disposed at an incline relative to horizontal. Such a pumping assembly is shown in FIG. 1. The assembly includes a pressure vessel 20 containing an entire submersible pump assembly 23. The submersible pump assembly includes a submersible electric motor 25 and a centrifugal pump 29 having inlet 31. The jacket has an inlet 13 connected to a pump 19 and a fluid tank 21. The pump is connected to a discharge conduit 33. The pump is typically a self contained electric submersible pump which is disposed in the pressure vessel or jacket. The above described assembly is further described in U.S. Pat. No. 5,203,682, entitled xe2x80x9cInclined Pressure Boost Pumpxe2x80x9d, which is incorporated herein by reference in its entirety.
While the forgoing apparatus is effective in providing pressurized fluid from the surface of a well in an environmentally sensitive way, it still suffers form some of the same problems of prior systems. Mainly, the apparatus includes the expensive, submerged electrical motors made for downhole, submerged use. Additionally, because the motors are included in the jacket, the electrical portions of the pump are also exposed to potentially corrosive and damaging fluids.
Therefore, there is a need for a simple surface pump which can be used to inject fluids, such as water, into a well at elevated pressure.
In one aspect, the invention provides a pump assembly comprising a pressure vessel housing a submersible pump, an industrial motor positioned adjacent the pressure vessel and having a shaft extending into the pressure vessel and connected to the pump. The pressure vessel has an inlet connected to a fluid source. The pump has an intake at one end and a discharge at the other end. A discharge conduit is connected between the pump discharge and a receiving vessel, such as a pipeline, well or tank. The pressure vessel may include a bleed off valve on an upper surface thereof and pressure relief valve. A mounting bracket or support mounts the pump assembly and may support the pressure vessel at an incline relative to horizontal or horizontal.